A massive hole in the ocean's floor opened (possible due to an earthquake or a storm of some sort) Which released the earth's core gases, this sent a HUGE bubble up through the ocean, at some ridiculously fast speed I am sure, (imagine farting in the bathtub) when this bubble hit the surface it was so big, and moving so fast, that ships, planes, fish, whales, literally ANYTHING in it's path would have been hit with this force, soaked in gases and water and possible drawn down to the bottom of the ocean or even into the gaping hole one it was done releasing gases and sealed back up by rock and sand over time. Something like this could easily have happened more than once over a long period of time.